In dental treatment of caries, the carious part is first removed, and then the lost part is filled with a curable composition in order to restore the shape and function of the tooth. Widely used examples of the curable composition for filling are composite resins, glass ionomer cements, and resin-modified glass ionomer cements, which are used in combination with dental adhesives. When the lost part is large, a restorative prosthesis called an inlay, an onlay, or a crown, which is produced from a metal, a ceramic, a cured composite resin or the like, is attached to the lost part. In attaching the restorative prosthesis to the lost part, a curable composition called a luting cement is used. Widely used examples of the curable composition for luting are compositions such as resin cements, glass ionomer cements, and resin-modified glass ionomer cements.
A restored part of a tooth needs to have long-term durability. To this end, it is required that the restorative material used itself, which is a cured product of a curable composition, be capable of stably maintaining its physical properties in the oral cavity over a long period of time, and that formation of a gap between the restorative material and the tooth be reduced to prevent secondary caries from occurring in the gap between the restorative material and the tooth. To meet these requirements, technical improvements have been attempted in terms of strengthening of the restorative material itself or strengthening of adhesion between the restorative material and the tooth structure.
It has been widely known that fluorine is effective in preventing the occurrence of caries, and there are disclosed techniques aimed at preventing the occurrence of second caries by endowing a restorative material with fluorine release ability so as to strengthen the surface of a tooth that is in contact with the restorative material as well as by reducing the formation of a gap between the restorative material and the tooth with improved bonding technology.
Fluorine is a useful substance for strengthening a tooth structure; however, under recent circumstances where a restorative method with the least possible use of teeth scraping is increasingly demanded for conservation of teeth, metal ion release from a restorative material is also demanded in treatment of early caries or restoration to a condition with slight remaining caries in order to restore a tooth tissue by remineralization or increase the strength of the tooth tissue.
Conventionally-known approaches for endowing a dental curable composition with metal ion release ability include addition of a water-soluble metal salt and addition of a metal ion-releasing filler (see Patent Literature 1 and 2). In the case of the addition of a water-soluble metal salt, metal ion release can easily be achieved as a result of dissolution of the water-soluble metal compound in a liquid such as saliva; however, there is a problem in that the physical properties such as the mechanical strength and bond strength of the cured product of the dental curable composition (restorative material) are markedly deteriorated with the leaching of the metal ions, leading to fracture, detachment or the like of the restorative material. In the case where a metal ion-releasing filler with low solubility in water is added so as to avoid the deterioration in the physical properties of the restorative material, the amount of ions leached from the restorative material is small, and effective action on strengthening of a tooth structure cannot be obtained.
A combination of hydroxyapatite particles with a calcium sugar phosphate is known to be effective in treatment of relatively early caries such as C1 and C2 caries, root caries, hyperesthesia, etc. (see Patent Literature 3). The technique described in Patent Literature 3 consists of restoring a tooth by injection or application of a hydroxyapatite particle-containing composition to a damaged part of a tooth surface, followed by impregnation with a calcium sugar phosphate-containing composition to bond the hydroxyapatite particles together via the calcium sugar phosphate. That is, the technique described in Patent Literature 3 is one established merely by combined use with hydroxyapatite particles, and lacks the technical idea of adding a curable component to a composition.
There is also known a sugar phosphate capable of reacting with a mineral to form a complex (see Patent Literature 4). Additionally, Patent Literature 4 discloses an oral composition containing the sugar phosphate. The oral composition described in Patent Literature 4, however, is one that undergoes formation of a complex of the sugar phosphate with calcium and thereby prevents the occurrence of calculus due to deposition of calcium on teeth. That is, the technique relates to inhibition of calcification involving calcium.